It has been previously suggested to have a single beam laser printer with the capability of switching its print resolution from 600 dots per inch (dpi) to 1,200 dpi, for example. Increasing the resolution of a single beam laser printer from 600 dpi to 1,200 dpi has necessitated reducing its print speed at 1,200 dpi to one-half of the print speed at 600 dpi. This print speed relation is based on the maximum mirror motor speed.
It also has previously been suggested to increase the throughput of a laser printer by using two beams to print two adjacent lines on a recording medium. This enables the throughput to be increased without requiring the speed of the mirror motor or the facets of the mirror to be increased.
When using a printhead with two laser beams, the distance between the centers of the two laser beams must be 42 microns for 600 dpi resolution and 21 microns for 1,200 dpi resolution. Therefore, if the dual laser beam printhead is to have its resolution changed from 600 dpi to 1,200 dpi, one of the two laser beams must be turned off, and the print speed must be reduced to one-fourth of the print speed of the 600 dpi resolution. This is because one of the two laser beams writes all of the odd numbered raster lines while the other of the two laser beams writes all of the even numbered raster lines. If one of the laser beams were not turned off and the print speed not reduced to one-fourth of the print speed at 600 dpi resolution, the even numbered raster scans would fall on top of the odd numbered raster scans at 1,200 dpi.
Thus, the increase in a dual beam laser printer resolution from 600 dpi to 1,200 dpi has necessitated reducing the print speed at 1,200 dpi to one-fourth of the print speed at 600 dpi. This is a significant reduction in print speed and is readily noticed by a user so as to not be satisfactory.
For example, a single beam laser printer might print at 24 pages per minute (ppm) at 600 dpi and 12 ppm at 1,200 dpi. A dual beam laser printer might print at 40 ppm at 600 dpi but only at 10 ppm at 1,200 dpi when operating at a print speed of only one-fourth of the 600 dpi print speed. Accordingly, a dual laser printer capable of printing at two resolutions would be at a commercial disadvantage with this significant reduction in print speed of 75% since its print speed at 1,200 dpi would be less than a single beam laser printer at 1,200 dpi.